Carroll Overton Alley, Jr. (June 13, 1927 – February 24, 2016) was an American physicist. He served as the Principal Investigator on the Apollo Program's Lunar Laser Ranging Experiment, which significantly restricted the possible range of spatial variation of the strength of the gravitational interaction. Alley was a PhD student of Robert Henry Dicke. Alley’s goal was nothing less than understanding quantum mechanics, gravitation, and relativity. His lifelong research interests included experimental and theoretical questions about the foundations of gravitational and quantum physics.